1. Field of the Invention
This invention relates generally to the field of consumer packaging. More specifically, this invention relates to plastic containers of the type that are used to package consumer beverages, and the strength characteristics of such plastic containers.
2. Description of the Related Technology
Plastic containers are in wide use commercially throughout the world for packaging liquids of all types, including consumer beverages. The most common type of plastic container that is used for packaging, for example, soft drinks, is fabricated from polyethylene terephthalate (PET) and is molded into a desired shape using a blowmolding process that is well known in the industry.
In the design of such containers, a number of factors are ordinarily considered. The container must be chemically resistant and should be shaped to avoid concentration of stress that result in unwanted failure. In addition, the container must be strong enough to endure the packaging process and subsequent handling during the gross packaging, shipping and retail display stages.
One type of strength that plastic containers are regularly evaluated for it is that of top load strength. Top load strength involves resistance to failure, typically sidewall buckling, when a vertical force is exerted onto the top of the container. Such vertical force is exerted onto the container during the filling process and when the closure is installed onto the container. In addition, a great deal of vertical force may be exerted onto filled containers when cases of the containers are stacked during shipping. Another type of strength that is regularly evaluated in the design of plastic containers is hoop strength. Hoop strength is the resistance provided by the container against the tendency of the container sidewall to bow outwardly or deflect inwardly when the contents of the container are under pressurization or when external forces are applied to the outside of the container, which of course is a common scenario in the packaging and transportation of carbonated soft drinks.
It is generally known in the industry that circumferential reinforcement such as ribbing tends to increase hoop strength, and that vertical reinforcement has a favorable effect on top load strength. However, it should be understood that there is a to economic disincentive to provide any more reinforcement to a plastic container design than is absolutely necessary, because increased reinforcement tends to make the container heavier and thus more expensive to manufacture. A need exists, then, for a plastic container design that optimizes hoop strength and top load strength while minimizing the amount of plastic material that is necessary to fabricate the container.